In an interview with The Chronicle, the 33-year-old co-founder of the popular San Francisco review site took aim at Google and suggested that e-mail deal services like Groupon often don't meet their customers' needs.

Yelp itself is on a bit of a tear.

The site's users and postings more than doubled in the last 18 months, topping 63 million and 21 million, respectively. Last month it launched services in Italy and Switzerland, putting it in 11 countries. And it's quickly approaching 1,000 employees, stretching the seams of its Mission Street headquarters.

The 7-year-old company has managed to make headlines in recent months, pushing for a tax break on stock options in San Francisco and floating a trial balloon about an initial public offering in the Wall Street Journal.

And so it seemed high time to sit down and catch up with Stoppelman.

He declined to talk about IPO plans or comment on the company's financials. But he did address Yelp's rapid growth and looming challenges. That includes the rise of competitors gunning for their primary customer: the local advertiser.

Yelp has made rare online headway tapping into the huge but fragmented pool of small and medium-size businesses, largely by luring millions of users happy to crank out and make use of free reviews. They represent an advertiser's dream of select customers expressing clear interest in local businesses like restaurants, salons, boutiques and the like.

But other businesses are piling onto the local ad space from different directions, including Groupon, Foursquare and Google.

Stoppelman explained why he believes Yelp has an edge on the competition and how it's "closing the loop" for local business.

Q:The local ad space has seen mounting competition from companies like Groupon, Google and Foursquare. How do you see this sector shaking out in the months or years ahead?

A: The topic of conversation lately has been sustainability: Who is here for the long term? Yelp has been in this business since it really became something worth thinking about in 2004, when the transition started happening from the world of the Yellow Pages to the world of searching online for local information.

Thanks to our community that has grown up in cities across the U.S., we now have some of the best content when it comes to trying to determine who is doing a great job from a local business standpoint. There is nowhere on the Web that is a better place to find that out.

Obviously there's been this explosion and questioning of the e-mail deal space, like Living Social and Groupon.

It's something we've done and had some success with. But we're not just sending out e-mails and hitting a lot of users who might not be interested.

We think it's far more competitive to have those deals live on the site, offering a discount for a cash amount, say $10 or $20 off at a popular restaurant. We think that's more sustainable for business owners; they're not giving away the store.

Q:Is your take that the ads are more targeted, in that you're reaching people who have navigated to a particular page through a search, as opposed to people that signed up for Groupon deals, once, say six months ago?

A: A lot of what Groupon is generating is demand for something people didn't know they wanted. I didn't know I wanted a massage, but if it's only $40, I'll just take it because it's so cheap. But there are millions of people on Yelp every day telling us what they want: "I'm looking for a taqueria. I'm interested in a burrito."

One of the challenges of buying local advertising is, how do you know if it worked? How do you know if it's got value? We're moving toward an e-commerce experience for local, an Amazon-like experience for local. It really closes the loop for local businesses.

Q:You've been one of the most outspoken critics of Google's practices. Last month, you told Congress that it's a monopoly that is abusing its strength in a way that undermines entrepreneurialism. What's the appropriate remedy in your view?

A: I'm not in a position to decide who should do what. We've been contacted, obviously, by a variety of regulators and interested parties from the government and we've simply been responsive.

Even prior to that, I think we've been quite open with our concerns about how we feel our content should be used. For us, the key problem is preferencing, it's not search ranking.

Once Google recognized that this is a potentially lucrative advertising space, they decided to create an opportunity of their own. Over time they've gotten more and more aggressive at showcasing that property (above the search results), regardless of whether it had relevant content. They've even gone so far as to take our content to power it.

Q:What did you make of Google's recent acquisition of Zagat? Does that make them a more formidable threat to your business?

A: I think it's an admission of continued failure, actually. Pretty much every six to 12 months there's a major announcement by Google when it comes to the local space: Google Maps, Google Local, Google Places. That was reinvented as Hotpot, and now we have Zagat.

So that's the new story for the year, but I read a good analogy on TechCrunch: Would you respond to Wikipedia by buying Encyclopedia Britannica? I think that's apropos.

Zagat was a sort of pre-Internet version of Yelp. But the fact of the matter is it's still built by sending out surveys, compiling them by hand with editors and producing it in a book.

I think Yelp represents the future, and it's at a scale that will be very difficult for Google to ultimately compete with.